The most important element in the design of television images is light. Apart from its fundamental role of illuminating the subject, light determines tonal differences, outline, shape, colour, texture and depth. It can create compositional relationships, provide balance, harmony and contrast. It provides mood, atmosphere and visual continuity. Light is the key pictorial force in television production.
The basic requirement to provide adequate light for a correctly exposed picture with the required depth of field can easily be achieved. Video cameras are sufficiently sensitive to provide an acceptable exposure under almost any found lighting condition. But whereas the television technical requirements of exposure, appropriate colour temperature and contrast range may be readily satisfied, the resultant image may be a muddle of competing areas of light and shade that do not communicate the intended ‘visual message’ of the shot. The control of light to guide the audience’s attention and to communicate production requirements plays a crucial part in the creation of any film or TV image. In almost every situation, visual communication can be more effective by choosing the camera position or staging participants with reference to found light or, if necessary, by adding some form of additional light.
The nature of light
Using a visual medium is choosing to communicate through pictures and in television, the end result of manipulating lens, camera position and lighting must be images that are compatible with human perception. A basic understanding of how we see the world will help when devising the lighting and composition of a shot. There are significant differences between how the eye responds to a scene and how a camera converts light into an electrical signal. Lighting must take account of these differences and make the appropriate adjustments.
One aim of lighting is to create a range of tones, either to conform to the contrast ratio of television or to express a production requirement. The relative brightness of a reflective surface is a subjective perceptual construct depending on the brightness levels of surrounding surfaces. Human perception responds to equal changes in brightness levels in a logarithmic manner and this can be mimicked by changes in grey scale step brightness. As we have discussed in Colour temperature (page 64) the eye continually adapts to changes in colour and has a much wider ability than a video camera to see detail in shadows through to highlights.
Inverse square law
Doubling the distance from light to subject quarters the level of illumination (lux) falling on the subject.
Cosine law
If the angle of a light beam to a surface it is illuminating is less than 90°, the illuminance of that surface is reduced by a factor equal to the cosine angle of incidence, e.g. for 30° angle of incidence, illuminance is reduced to 86% (cosine 30° = 0.86).
Incident light meter
These meters are designed to measure the light falling on the subject. To calculate the ratio between key and fill, place the meter close to the face of subject and point in turn at the key light and the fill. The ratio of the two readings will provide the contrast ratio of light on the face.
Like clay in a potter’s hand, the four characteristics of light, quality (hard or soft), direction (frontal, side, back, underlit, top lit, etc.) source (available light, additional lights), and colour can be manipulated by the lighting cameraman to achieve the precise requirements for a specific shot. The auto features on a camera are often unable to discriminate the priorities of a shot and must be over-ridden, so likewise, to simply accept the effects of a found lighting situation is to disregard the most powerful part of image making. Available or ‘found’ light is any combination of sunlight and/or artificial light that illuminates any potential location.
Quality
The quality of light produced by a natural or an artificial light source is often categorized as ‘hard’ or ‘soft’. A ‘point’ source (i.e. a small area of light at a distance from the subject) produces a single hard-edged shadow. An unobscured sun or moon is a hard light source. Hard lighting reveals shape and texture and when produced by a lamp, can be shaped and controlled to fall precisely on the required part of the frame. Shadow areas of an image (the absence of light or very low light levels) often play an essential part in the composition and atmosphere of a shot. Lighter and darker areas within the frame help to create the overall composition of the shot and to guide the attention of the viewer to certain objects and actions. Shadows on a face (modelling, see page 181) reveal structure and character.
A soft source of light can be produced by a large area of light (relative to the subject) and produce many overlapping soft-edged shadows and tends to destroy texture. It is not so controllable as hard light but is often used to modify the effect of hard light, for example, by bouncing sunlight off a large area reflector to fill in the shadow created by sunlight falling on the subject.
How much light is used and where it is focused also sets the ‘key’ of the image. A brightly lit shot with little or no shadow is termed a high key picture and is usually considered cheerful and upbeat. An image with large areas of shadow and very few highlights is termed a low key image and appears sombre, sinister or mysterious.
Direction
The direction from which any part of an image is lit affects the overall composition and atmosphere of a shot (see also Lighting a face, page 180). Frequently when setting lamps for a shot, the position and therefore the direction of illumination is controlled by the perceived ‘natural’ source of light (e.g. window or table lamp in an interior).
Early film was lit by natural light. Artificial light sources were introduced for greater production flexibility and economic reliability (e.g. to keep filming whatever the weather). A system of lighting faces (often the most common subject in feature films) was devised using a key light to model the face, soft light to modify the key light effect and a backlight to separate the face from its backing. Three-point lighting is still extensively practised although the use of a backlight has fallen out of fashion in feature film making. The quest for a ‘natural’ look to an image produced a fashion for using large areas of bounced light. Modelling on a face was reduced or eliminated and the overall image produced was softer and less modelled. To heighten realism, and because of the availability of very sensitive cameras, many shots were devised using available light. This is often necessary when shooting documentaries because not only does rigging lights take time and unsettle participants but being filmed under bright lights is inhibiting and counter-productive to the aim of recording unmediated ‘actuality’.
The fourth aspect of lighting is colour, which is discussed on page 177. See also mixed light, page 184.
Brightness
How ‘bright’ one subject appears compared to another and the perceived changes in brightness is a function of perception. In an interior, a face against a window during the day will appear to be dark. With the same illumination on the face against a window at night, the face will appear to be bright. Colours appear to be lighter against a dark background and darker against a light backing.
A grey scale chart is designed to mimic perception by having a series of grey tones starting at peak white and decreasing by 1/√2 to produce equal changes in brightness to the eye. This logarithmic progression is similar to the ear’s response to equal changes in sound level (see page 188). Starting at 60% reflectivity and decreasing by 1/√2 (0.5 of one stop) produces (in this design of grey scale) 9 wedges with 0.8% black represented by a chip in the chart lined with black non-reflective flock paper or velvet. The background is often 16–18% reflectance to simulate average scene brightness.
How light is shaped, balanced and distributed within a shot plays a vital part in television production but there are a number practical considerations when deciding the overall level of light that is to be used. These include:
■ satisfying exposure requirements which depend on camera sensitivity;
■ creating an appropriate depth of field;
■ providing a good environment for artists’ performance;
■ heat generation, ventilation, number of luminaires available, total capacity and cost of the power supply.
Camera sensitivity
Camera sensitivity is usually quoted by camera manufacturers with reference to four interlinking elements – a subject with peak white reflectivity, scene illumination, f number, and signal-to-noise ratio for a stated signal. It is usually stated as being the resulting f number when exposed to a peak white subject with 89.9 per cent reflectance lit by 2000 lux and also quoting the signal/noise ratio. For most current cameras this is f 8, with some achieving f 11 and better. The definition is based on the Japanese standard for peak white reflectivity of 89.9 per cent. The rest of the world mostly use a 60 per cent reflectance peak white based on the need to correctly expose (Caucasian) face tones without overloading (overexposing) on a peak white area. With a 60 per cent reflectance surface, 2000 lux will only allow it to be two thirds exposed therefore the illuminance has to be increased to 3000 lux to transpose the sensitivity rating to 60 per cent peak white operation. The sensitivity of the camera could be increased by simply greater and greater amplification of weak signals but this degrades the picture by adding ‘noise’ generated by the camera circuits. In many ‘actuality’ location work (e.g. news gathering, sports coverage, etc.), the gain of the head amplifiers can be increased if insufficient light is available to adequately expose the picture.
Depth of field
Lighting level will determine f number for correct exposure, which in turn will decide depth of field (see Zooming, page 50). The range of subjects in focus within the frame will have a significant effect on the visual appearance of the production. The chosen depth of field can therefore be a production design element as well having a crucial impact on the ability to find and hold focus in ad-lib camerawork. Other factors which affect exposure include shutter speed, lens range extenders, zoom ramping, filters, prompt devices and the lighting environment to accommodate performance and mood.
Mood and atmosphere
With highly sensitive cameras, it is possible to achieve correct exposure with very low light levels – levels which may appear to be darker than a brightly lit office corridor. This may be appropriate for some types of location work but it can have a depressing effect on other types of production. A location should be lit at a level that provides a good environment for participants and enhances their presentation. The opposite consideration, of high intensity key lights close to the eyeline, can also inhibit optimum performance and is usually avoided in documentary work.
Luminaires require a power supply and, in an enclosed space, some method of ventilation to extract the heat that tungsten lamps can generate. Also the number, hire cost of luminaires available to a production and the total capacity of the power supply and the deployment of the rig are practical controlling factors in lighting design.
Use of colour
The individual response to colour may be a product of fashion and culture – a learnt relationship – or may be an intrinsic part of the act of perception. People’s colour preferences have been tested and in general western people choose in order of preference blue, red, green, purple, orange, yellow. This choice is modified when the colour is associated with an object that has a specific use. Below is a very generalized checklist of points to bear in mind when using colour:
■ Many colours have a hot or a cold feel to them. Red is considered hot and blue is felt as cold. It will take other strong design elements within a shot to force a foreground blue object to exist in space in front of a red object. The eye naturally sees red as closer than blue unless the brightness, shape, chroma value and background of the blue is so arranged that in context it becomes more dominant than the desaturated, low brightness of the red.
■ Colour effects are relative and no one set of guidelines will hold true for all colour relationships. For example, the intensity of a hot colour can be emphasized by surrounding it by cool colours. The intensity of the contrast will affect balance and to what part of the frame the eye is attracted.
■ The perception of the apparent hue of any coloured object is likely to vary depending on the colour of its background and the colour temperature of the light illuminating it. Staging someone in a yellow jacket against green foliage will produce a different contrast relationship to staging the same person against a blue sky.
■ Complementary contrast balance can be achieved by opposing a colour with its complementary. The complementary of red is green, the complementary of blue is orange, the complementary of yellow is violet. These complementary pairings consist of a hot and a cold colour. Complementaries placed alongside each other will appear to be more vivid and vital than colours that are adjacent in the colour wheel. Visual equilibrium however is not simply achieved by equal areas of complementary pairs. Blue needs a greater area to balance its complementary orange. Red needs approximately the same area of green whereas yellow needs a relatively small area of violet to achieve visual equilibrium.
■ Colour can communicate experience or feeling by association. Red is often described as passionate, stimulating and exciting. Blue is seen as sad and depressing. Yellow is serene and gay whilst green is thought of as restful and stable. Strong prolonged stimulation of one colour has the effect of decreasing the sensitivity to that colour but sensitivity to its complementary is enhanced.
■ The balancing of area and the shape of a coloured object has a strong impact on the unity of an image. A small area of intense colour can unbalance a composition and continually attract the eye. If its location coincides with the main subject of the shot then the right emphasis is achieved. If it exists near the edge of frame or away from the dominant subject then it acts as a second subject of interest and is a distraction.
■ Paintings often achieve a strong visual impact by restricting the range of colours used. A limited palette of colours on a set can create unity and impact. A number of sequences in a variety show can each be given their own individual identity by using colours which complement or contrast with the artiste’s costume colour
Reflector: A reflector board or sheet requires no power and takes up very little space. It is invaluable for fill-in lighting by bouncing light from daylight or lamp into shadow.
Battery lamps: These are fixed to the top of the camera and powered from the camcorder battery or, preferably, a separate battery belt. When working in daylight they require a dichroic filter to correct the colour temperature of the lamp to daylight. A dichroic is made of glass and is therefore more fragile than gel filters, but their advantage is that they transmit approximately 15 per cent more light than gels.
Flight kit (portable lighting kit): This is a two or three lamp kit that derived its name from its compact size small enough to fit into a metallized container for quick stowage and easy transportation.
Redhead: This is a 800 W lamp drawing 3.3 A, weighing 3 kg including barndoor and safety glass, with an output of approximately 6000 candelas (cd) flooded and 24 000 cd spotted and a wide beam angle >80°.
Blonde: This is a 2000 W lamp drawing 8.3 A and weighing 6 kg with barndoor and safety glass. It produces approximately 25,000 cd flooded and 150,000 cd spotted and a beam angle >80°. Because of their weight and flexibility and their low power consumption they can be rigged and derigged quickly and plugged into most domestic power supplies.
Discharge lamps: Discharge light sources such as HMI lamps produce light by ionizing a gas contained in the bulb. They have greater efficiency than tungsten, are lighter and cooler in operation and produce light which approximates to daylight. They require an EHT supply to ionize the gas and a current limiting device. This may be a simple inductive choke or in the form of a flicker free electronic ballast. A 1.2 kW HMI, which is one of the most useful lamps on a small unit, with conventional ballast, will draw 12 A when switched on but settle to 6.4 A when warmed up. It can therefore be used on a domestic 13 A ring main circuit providing no other lamps are connected when it is switched on.
With fluorescent lights, the use of high-frequency dimmable ballasts operating above 40 kHz provide a flicker free output and allow dimming with a simple 0–10 V control (or 100 kΩ potentiometer) to achieve reduction in lighting levels with little change in colour (unlike dimmed tungsten sources).
Fluorescent tubes, HMI discharge lamps and neon signs do not produce a constant light output but give short pulses of light at a frequency depending on the mains supply. Using a 625 PAL camera lit by 60 Hz mains fluorescent (e.g. when working away from the country of origin mains standard) will produce severe flicker. Some cameras are fitted with 1/60th shutter so that the exposure time is one full period of the lighting. If a high shutter speed is used, the duration of the pulsed red, green and blue parts of the light spectrum may not coincide with the ‘shutter’ open and a colour drift will be observed to cycle usually between blue and yellow. It can be eliminated by switching the shutter off. FT sensors have a mechanical shutter which cannot be switched off and therefore the problem will remain. The problem with most fluorescent tubes is that they emit very little or no red and an excessive amount of green in comparison to daylight. For example, light from mercury vapour lamps is blue-green with no red in it, and no amount of filtering can add red to it. Unless red light can be added to the scene, there is no hope of getting a video image that looks normal. Conversely, low pressure sodium vapour lamps contain nothing but yellow light which cannot be colour corrected.
High-frequency fluorescent luminaires (cold lights)
Fluorescent luminaires are now being used for television programme production. Usually several lamps are grouped to produce a practical light source, hence they are soft sources. Control of the light beam shape is either by a fine structured ‘egg-crate’ or ‘honeycomb’ fitment. Improved phosphors have made the fluorescent lamp acceptable for television and film and are available to provide tungsten matching and daylight matching colour temperatures.
Filters and diffusers
■ Neutral density filters: A recurring problem with location interiors is controlling and balancing the intensity of daylight from windows with the much lower light levels from lamps. Neutral density (ND) filters will reduce the level of daylight without changing its colour temperature. They are made of flexible gelatine or thin acrylic sheets and are available in a range of grades. They can also be combined with colour correction filters. The filters are fixed to windows in a method that will avoid being seen on camera. Although ND gel can buckle and produce flares, it is easily transportable in rolls. The acrylic sheet needs to be cut, is difficult to move and is expensive.
■ Plastic ‘scrim’, a perforated material silver on one side and black on the other, can also be used on windows (black side in) to act as a neutral density filter (0.6ND). It is more robust than ND gels and not so prone to flare. Check that its perforated pattern cannot be seen on camera.
■ Polarizing filters on the camera lens reduce glare reflections, darken blue skies and increase colour saturation. They are useful in eliminating reflections in glass such as shop windows, cars and shooting into water. The filter must be rotated until the maximum reduction of unwanted reflection is achieved.
■ Spun or diffusion, a fibreglass-type material, is used in front of lamps to diffuse or soften the light. It also reduces the lamp intensity. It can be used to cover partially a portion of the lamp’s throw to soften edges and to produce a reduction in brightness in part of the shot. It is available in a range of grades and can be doubled up in use to increase diffusion.
■ Colour filters: Polyester filters have a clear plastic base coated with a coloured pigment. Polycarbonate filters have the base material mixed with the pigment. They are referred to as high temperature (HT) filters and are not affected by heat as much as the polyester filters.
■ Colour correction filters are used to correct the light sources to a common colour temperature, e.g. tungsten sources to daylight (5500K), daylight to tungsten (3200K) or to correct both sources to an intermediate value.
■ Barndoors are metal flaps fitted to the front of the lamp lens and can be adjusted in a number of ways to keep light off areas in shot and to shape, soften and produce gradations on surfaces.
As we discussed in Exposure continuity (page 76), in general, Caucasian face tones will tend to look right when a ‘television white’ of 60 per cent reflectivity is exposed to give peak white. As a generalization, face tones are approximately one stop down on peak white. But as well as achieving correct exposure, lighting a face also involves making decisions about how a specific face is to be portrayed. Most professional presenters know their ‘good’ side and their ‘bad’ side. This may be to do with blemishes or their nose line but usually it is because faces are asymmetrical about the centre-line. Depending on its position, the key light modelling will either make the shadowed side of the face appear to be narrower (to be avoided if it is already the narrow side of the face) or broader.
The lighting treatment must take into account blemishes (‘key’ into the blemish), emphasizing or adjusting the overall shape of the face, the shape of the jaw line, the line of the eyes, the line of the mouth, etc. If a subject with a bent nose is keyed the same way as the bend of the nose, this will exaggerate the nose bend. If keyed in the opposite direction it will tend to straighten out the bend. The American cinematographer Gordon Willis used top lighting on Marlon Brando in The Godfather to help reduce Brando’s jowls but this also had the effect of putting his eyes in shadow and making him more mysterious and threatening. Presenters with deep set eyes can lose contact with their audience unless a way is found to get light on to their eyes. A catch light reflected in the eyes often lifts the personality of the face and allows the viewer ‘eye contact’ with the most important part of the face.
Location lighting may only have to accommodate one face and one camera position, but the shot may include a natural lighting source such as a window or the direct light from the sun (see Mixed light, page 184). Ideally, the aim is to light artistes separately to their backgrounds as this enables control of the lighting of both areas to be achieved.
Key light
A single strong directional light gives the best modelling and structure to a shot. The key light provides the necessary exposure and brings out the three-dimensional aspects of the subject. As we have discussed, when keying faces, the decisions to be made are: where should the nose shadow fall (or should there be a nose shadow?), are deep-set eyes lit, does the angle and position of the key suit the structure of the subject’s face, are there reflections in spectacles, and are any facial imperfections exaggerated or concealed? Does it throw unwanted shadows on the background of the shot?
Fill
Wherever the key is placed, the strong shadows it creates need to be modified to reduce the contrast range and normally to lighten the mood of the shot. This is achieved by a fill light on the opposite side of the lens to the key. It is usually a soft source of light produced by a reflector or a diffused flooded lamp or an overcast sky but not direct sunlight. The key-to-fill ratio on the face is the contrast range and can be balanced by using a meter or estimated by eye to match the required mood of the shot. An average is between 2:1 and 3:1.
Backlight
It is usually necessary to find some visual way of separating the subject from its background so that attention can be focused on the subject. Check for suitable unobtrusive background detail when positioning camera and subject and use a hard light source directed from behind the subject to highlight the head. This will give sparkle to the hair and rim light the shoulders. Try to avoid too high an intensity – the backlight should hardly be perceptible.
Background light
To avoid people being shot in limbo, some light needs to be directed to the space behind them. The aim should be to light sufficient background to provide some indication of location whilst avoiding overpowering the foreground. A lit background gives space and mood to the shot but on location, ensure that it conforms to the main source of light.
Whether shooting interior or exterior, a fundamental problem with location work is dealing with a mixture of light of different colour temperatures. If the light remains uncorrected, faces and subjects may have colour casts which look unnatural and distracting. The two most common light sources on location are daylight, which has a range of colour temperatures but averages around 5600K, and tungsten light which is often produced by lamps carried to the location which are approximately 3200K.
Colour correction filters
There are two basic types of correction filter used when attempting to combine mixed lighting of tungsten and daylight.
■ An orange filter which converts daylight to tungsten and is most often seen attached to windows for interior shots.
■ A blue filter which converts tungsten to daylight and is often used on tungsten lamps.
Any correction filter will reduce the amount of light it transmits and therefore a balance must be struck between colour correction and sufficient light for adequate exposure. A filter for full colour conversion from daylight to tungsten will have a transmission of only 55 per cent which means nearly half of the available light is lost. A filter for full colour correction from tungsten to daylight has an even smaller transmission factor of 34 per cent – it cuts out nearly two thirds of the possible light from a lamp. This is a more serious loss because whereas daylight is usually more than adequate for a reasonable exposure, reducing the light output of a lamp (say a redhead) by blue filtering to match daylight may leave an interior lit by blue-filtered lamps short of adequate light.
All light sources at same colour temperature
The choice when shooting an environment which has a mixture of daylight and tungsten is to decide whether to correct all sources to daylight or all sources to tungsten. If the choice is tungsten, any window which is in shot or producing light which is reaching the shot requires filtering. It needs a full orange filter squeegeed onto the glass or fastened by double-sided tape onto the frame. Orange filters can be obtained which have additional light reduction by combining with neutral density filters. This is helpful when attempting to balance out a very bright window with the interior lit by lamps.
Daylight
If the choice is to light by daylight, then all lamps must be blue filtered to correct them to daylight (5600K) and a careful check made on any table lamps or domestic lighting which may influence the shot. The disadvantage of choosing daylight is the reduction in light output due to the filters and the increased contrast range between subjects lit by a combination of daylight and colour corrected tungsten. Neutral density filters without colour correction can be used on windows to reduce the intensity of daylight and to achieve exposure on external detail.
Mixed light
A recurring location item is the interior interview. It usually requires shots of the interviewee seated in his or her office or house being questioned by a presenter.
Interview position
There are a number of questions to be answered before deciding camera position and interview position:
■ Is there a colour temperature difference and balance between daylight entering from windows and the light provided by added lamps?
■ Do windows need to be in shot?
■ Does the interview position allow a variety of shot to sustain a long interview if required?
■ Can the relationship of people be shown?
■ Is the environment of the interviewee important to the interview?
■ Does the background to the shot give more information about the topic?
■ Is there a comfortable distance between participants to allow them to relate to each other?
■ Is there sufficient space in the chosen location and how convenient is it to relight and reposition for reverses?
The first decision to make is whether to go tungsten or daylight. If daylight is consistent and there is no direct sunlight on the proposed interview area, then colour correcting for daylight is the best option, using daylight as the main source.
If sunlight is entering the room and if it is intermittent, then avoid windows in frame and light by tungsten filtering or curtaining out the large changes in brightness from the sun.
Position the camera close to the shoulder of the interviewer with the lens at approximately seated eye-level to get a good eyeline on the interviewee. Light for that position checking for a good fill ratio and if the background is adequately lit. Switch off any fluorescent lighting, if possible, and check sound level for background noise. Check exposure, white balance and voice levels and record the interview. Only reframe on interviewee during questions unless a move has been agreed. Keep the camera recording after the interview has ended. Sometimes, a vital comment is made at the end.
After confirming that no more questions are to be asked, reposition the camera for a 2-shot checking that there has been no significant change of posture or any other continuity links between single and 2-shot. Record the 2-shot with the interviewer repeating some of the questions.
Reposition and relight for the interviewer’s questions and noddies, staying on the same side of the imaginary line between interviewer and interviewee as the shot of the interviewee.
More haste
Location recording is often a scramble to rig, record, wrap and move on to the next set-up. There is always the urgency to get the job done, but, as pressurized as this may be, it is never expedient to cut corners on safety. A couple of minutes saved by not making safe a cable crossing the top of a flight of stairs may result in injury and many hours of lost time. You have a responsibility to ensure that the condition and the method of rigging lamps and cables at a location is safe to yourself and to members of the public.
Periodically check the earthing and safety of your lamps. Make certain the safety glass or wire is fitted and not damaged in any way. Check the condition of cables for frayed or worn insulation and that they are earthed correctly.
HMIs
Discharge light sources such as HMI lamps produce light by ionizing a gas contained in the bulb. Because of a high bulb pressure they are liable to explode and they also produce a harmful level of ultraviolet radiation. Therefore all discharge sources must be fitted with a glass filter as a safety glass. Usually an inter-lock will prevent the supply of EHT if the safety glass is broken or missing.
Check that any HMI you are using has a safety glass fitted.
Location electrical supplies
It is important to check the power supply fuse rating and the condition of the wiring before using a domestic supply. Blown fuses can waste time but burnt out wiring could start a fire. Also check cable runs, especially around doors and tops of stairs. Check where you place lamps. They get hot and so will anything touching them.
Care and consideration
If you need to attach any material to windows, use masking tape or low-tack tape so that you leave the paintwork as you found it. Remember, you may want to return to that location. If you have ever followed a TV crew that caused problems onto a site, you will appreciate that loss of goodwill from the public makes for a very hard day’s shoot. People appearing on television for the first time may be nervous or excited. You may be under pressure to get the job done and onto the next set-up. When working with the public, their safety and your safety are equally important.
Accidents and disasters
Police or authorities in control of an accident locale or disaster area may exclude you from the location if you are not wearing a protective (hard) hat and luminous ‘vest’. The requirement is in the interests of your safety as well as the interests of other people working on that site.